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John Dalton

John Dalton was born in a small thatched cottage in the village of Eaglesfield, Cumberland, England. That much is certain. What is less certain is the day and date of his birth as his family never recorded it properly in the family bible (the way it was done in those days). However, much later in life, he was told that it was September 5th, 1766, and that is the way history records it.

His family were Quakers, and had been for a long time. His Grandfather had converted to this religion in about 1695, about the time he got married. Dalton's father inherited an estate of about 60 acres and married a local Quaker girl, Deborah Greenup. John Dalton grew up working in the fields and in the family shop where cloth was made. His sister sold paper, ink and pens, but despite all these sources of income they were relatively poor and the boys did not get much formal education.

However, they did get a basic grounding in reading, writing and arithmetic at the nearest Quaker school, which meant that that they were doing better than most. In Dalton's time only about 1 in 200 people could read!

At the Quaker school, called Pardshow Hall one teacher - the "master" - called John Fletcher took a liking inspired the young Quaker boy to take up solving mathematical problems, a skill he quickly mastered. This brought him to the attention of a number of people, including a rich Quaker, Elihu Robinson, who mentored him in mathematics, science and meteorology.

a school of his own

After a failed attempt to start a school in his home town of Eaglesfield, John Dalton eventually went into partnership with his brother and in 1785 took over a different school in Kendal where the brothers offered a range of subjects including languages and 21 mathematics and science courses! Despite the school's popularity (they had 60 pupils at one point) the school did not make money and Dalton had to write answers to "ladies questions" in magazines to make needed extra income.

Another person who inspired, instructed and then mentored John Dalton was the blind son of a wealthy Kendal merchant who was very interested in a range of scientific subjects, including optics. John Gough clearly had a significant influence on John Dalton, as the first two books that Dalton published were dedicated to his friend and mentor.

keeping good records

One suggestion that Gough made to Dalton was to keep a daily log of the weather and matters meteorological. So he started writing down what he saw and what he measured about the weather patterns in a book, every day. He kept this journal for his entire life, and probably the very last thing he did on the day he died, was to make his final entry.

To make money he gave public lectures and even offered to sell his extensive, eleven volume botanical collection to a local museum, but it was John Gough who in 1793 pulled a few strings and got him a place as a tutor at Manchester College (called the 'New College' and founded by Presbyterians), where he earned 80 pounds a year. He had wanted to become a physician, but his family persuaded him that his bedside manner would keep him poor all his life, so he chose science instead.

going to Manchester

Manchester was probably the second largest town in England at that time, and was rapidly becoming the industrial center of the world. This is where the famous "industrial revolution" started and the town boasted colleges, libraries and lots of other intellectual stimulants. Dalton joined the Manchester Literary and Philosophical Society and immediately published his first book on Meteorological Observations and Essays.

In this book Dalton lays out for the first time his ideas on gasses, and that in a mixture of gasses, each gas exists independently of each other gas and acts accordingly. His famous ideas were starting to form.

However, after six years as a college tutor he went private. He gave up the post at the college and offered to tutor individual students privately at the sum of two shillings a session. This allowed him much more time to conduct his own research.

It was a good move, as he was able to think and perform a series of experiments at this time that led him to the "law" or partial pressures of gasses, which he published in an work entitled Experimental Essays on the Constitution of Mixed Gases; on the Force of Steam or Vapour from water and other liquids in different temperatures, both in a Torricellian vacuum and in air; on Evaporation; and on the Expansion of Gasses by Heat

a mixture of gasses

Here he explained to the world that if two gasses were mixed together they behave as if they were totally independent of each other. The first gas does not attract or repel the second gas, it just behaves as if the second gas did not exist. The result of this "independence" was that the total pressure exerted by the mixture of gasses was the sum of the separate pressures exerted by each part in the mixture.

He was also able to show that the environment had a measurable affect on the pressure shown by his gasses, and that there was a mathematical relationship between the pressure of a vapor and its ambient temperature.

Many historians think that Dalton chose to study gasses because of his interest in meteorology, a life long interest in which he collected over 200,000 observations. Even when trying to relax, Dalton could not, however, stop keeping records. One of his few methods of relaxation was to go to a pub called the "Dog and Partridge", just outside town. Every Thursday he would bowl heavy black wooden balls across a perfectly kept green lawn (the English call this game "Bowls") and try to hit a tiny white one. His hits, misses and other scores would be as meticulously recorded as his scientific data.

getting a reaction

Not all gasses interact harmlessly, as Dalton discovered. In 1803 he began to react a gas called nitric oxide (N0) with oxygen to produce a third type of gas. Strangely the result could come out in one of two ways depending on the proportions, or ratios, of the reacting gasses. Using one set of conditions it looked like nitrogen was combining with oxygen in the ratio 1 to 1.7, but at other times, in the ratio 1 to 1.3. By August 1803 he had the answer to this puzzle - the "law of multiple proportions" which stated that the weights of elements always combine with one another in ratios that were always whole numbers - thus:

2NO + O ---> N2O3
NO + O ---> NO2

In this way, Dalton was able to start working out a table of atomic weights based on the lightest element, hydrogen, having the arbitrary value of 1.

He expressed his ideas about the make up of gasses this way, "we may form an idea of this by supposing a vessel filled with small spherical leaden bullets among which a quantity of fine sand is poured. The balls are to the sand as the particles of bodies are with respect to the caloric; with this difference only, that the balls are supposed to touch each other, whereas the particles of bodies are not in contact, being retained at a small distance from each other by the caloric."

the right word

While forming these mental images of the physical composition of gasses, Dalton struggled to find words and images he could use to express his ideas. He found two solutions. From his reading of ancient texts, particularly those of Hindu origin, he found the term "atom eater" used by the author Kanda to describe discontinuous matter. Also that the philosopher Democritus had once described water as mostly empty space with smooth balls gliding over each other. The "balls" he called atoms. Newton also contributed the idea that "... God in the beginning formed matter in solid, massey, hard, impenetrable, moveable particles ..."

This seemed to be the answer. All matter was made up of hard round particles, which he called 'atoms', and that each type of atom, or element, such as hydrogen, oxygen, nitrogen, etc., differed from the next only by its weight.

The atomic theory had been born.

symbolic representation

But his next idea was one of equal genius; how to represent this idea symbolically so that tiny, invisible particles could be 'seen' and their combining properties studied.

The solution, so Dalton thought, was to draw circles, each circle representing one of his tiny atomic spheres. Each element could be distinguished by the contents of the circle, thus:

Using this symbolic representation of invisible atoms, their combining properties could be drawn out, played with, thought about, revised and corrected. It was the perfect way of creating a 'laboratory' where atoms could be moved around at will and placed in a series of relationships that could then be confirmed or denied by actual experiments or data. Today scientists are very comfortable with the idea of model building, and using real or computer models to help them prod and poke around an idea. But in Dalton's day this concept was a major breakthrough.

The union of atoms into higher order structures could also be represented, thus:

So chemical reactions could be studied on paper to see if they conformed to observed fact. A way was open that would take the messy mystery out of the nature of physical matter and make it possible to study its properties and behaviors in a rational and mathematical way.

weighty matters

On October 21st, 1803, Dalton stood before the Manchester Literary and Philosophical Society (or which he was now the Secretary) and announced to the world the relative weights of the atoms. This fundamental breakthrough in science did not go un-noticed, and he was immediately invited to repeat his announcements before the Royal Institution of London - before a much larger and much more distinguished audience. The word was out, and Dalton's atomic theory began to receive much publicity and debate.

Some scientists accepted the concepts at once; Thomas Thomson and William Hyde Wollaston. Some were skeptical for as long as 60 years; Charles William Eliot of Harvard University was still not convinced when teaching his classes in 1868. While some were down right hostile; Davy was fanatically opposed and even went as far as to mock the "tall, gaunt, awkward scholar" as Dalton was described by the father of William J. Mayo (who was one of Dalton's pupils).

But as more and more experimental work confirmed the theoretical work, even Davy in later life (about 50 years later) was forced to admit that Dalton was right and that all matter was atomic in nature.

the rewards of science

England is a country that does not like to reward its heroes, a trait that borders on the pathological at times and a theme that recurs in almost every field of endeavor, especially science. So, event though he was over 60 years old, he still had to teach arithmetic to private students to make a living. His friends tried to get him a modest pension from the Government, but were told "... it would be attended with great difficulty". It took a lot of begging and pleading by some influential persons before Lord Grey's government finally and reluctantly provided a modest means of support for one of it's more innovative scientists. It was only 150 pounds a year.

Science@a Distance
© 2002, Professor John Blamire